Purkinje cell
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2008-05-14T22:34:51Z
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Intro paragraph: Added "s" to end of "neuron"
{{Infobox_neuron
|neuron_name = Purkinje cell
|image_neuron = PurkinjeCell.jpg
|caption_neuron = Drawing of pigeon Purkinje cells (A) by [[Santiago Ramon y Cajal]]
|location = [[Cerebellum]]
|function = inhibitory projection neuron
|neurotranmitter = [[GABA]]
|morphology = flat dendritc arbor
|afferents = [[Parallel fiber]]s and [[Climbing fiber]]s
|efferents = Cerebellar deep nuclei
}}
''For the cells of the [[electrical conduction system of the heart]], see [[Purkinje fibers]]''
'''Purkinje cells''' (or '''Purkinje neurons''') are a class of [[GABA|GABAergic]] neurons located in the [[cerebellum|cerebellar cortex]]. They are named after their discoverer, [[Czech people|Czech]] [[anatomist]] [[Jan Evangelista Purkyně]].
==Anatomy==
[[Image:Gray706.png|thumb|200px|left|Transverse section of a cerebellar folium. (Purkinje Cell labeled at center top.)]]
These [[Cell (biology)|cells]] are some of the largest [[neuron]]s in the human [[brain]], with an intricately elaborate [[dendrite|dendritic]] arbor, characterized by a large number of [[dendritic spine]]s. Purkinje cells are found within the [[Purkinje layer]] in the [[cerebellum]]. Purkinje cells are aligned like [[domino]]s stacked one in front of the other. Their large dendritic arbors form nearly [[two-dimensional]] layers through which [[parallel fiber]]s from the deeper-layers pass. These parallel fibers make relatively weaker [[excitatory synapse|excitatory]] ([[glutamatergic]]) synapses to spines in the Purkinje cell dendrite, whereas [[climbing fibers]] originating from the [[inferior olivary nucleus]] in the [[medulla]] provide very powerful excitatory input to the proximal dendrites and cell soma. Parallel fibers pass [[orthogonal|orthogonally]] through the Purkinje neuron's dendritic arbor, with up to 200,000 parallel fibers forming a [[synapse]] with a single Purkinje cell. Each Purkinje cell receives a synapse from only a single climbing fiber. Both basket and stellate cells (found in the cerebellar [[Cerebellum#Molecular Layer|molecular layer]]) provide [[inhibitory]] (GABAergic) input to the Purkinje cell, with basket cells synapsing on the Purkinje cell axon initial segment and stellate cells onto the dendrites.
Purkinje cells send inhibitory projections to the deep cerebellar nuclei, and constitute the sole output of all [[motor coordination]] in the cerebellar cortex.
==Electrophysiological activity==
[[Image:CerebCircuit.png|thumb|right|200px|Microcircuitry of the cerebellum. [[Excitatory synapses]] are denoted by (+) and [[inhibitory synapses]] by (-).<BR>MF: [[Mossy fiber]].<BR>DCN: [[Deep cerebellar nuclei]].<BR>IO: [[Inferior olivary nucleus|Inferior olive]].<BR>CF: [[Climbing fiber]].<BR>GC: [[Granule cell]].<BR>PF: [[Parallel fiber]].<BR>PC: [[Purkinje cell]].<BR>GgC: [[Golgi cell]].<BR>SC: [[Stellate cell]].<BR>BC: [[Basket cell]].]]
Purkinje cells show two distinct forms of electrophysiological activity:
* '''Simple spikes''' occur at rates of 17 - 150 Hz (Raman and Bean, 1999) either spontaneously or and when Purkinje cells are activated synaptically by the parallel fibers, the axons of the granule cells.
* '''Complex spikes''' are rapid (>300 Hz) bursts of spikes caused by climbing fiber activation, and can involve the generation of calcium-mediated action potentials in the dendrites. Following complex spike activity simple spikes can be suppressed by the powerful complex spike input.
Purkinje cells show spontaneous electrophysiological activity in the form of trains of spikes both sodium- as well as calcium-dependent was initially shown by [[Rodolfo Llinas]] (Llinas and Hess (1977) and Llinas and Sugimori (1980. P-type calcium channels were named after Purkinje cells where they were initially encountered (Llinas et al 1989), which are crucial in cerebellar function. It has recently been shown that climbing fiber activation of the Purkinje cell can shift its activity from a quiet state to a spontaneously-active state, and vice-versa, serving as a type of toggle switch (Lowenstein et al., 2005, Nature Neuroscience). However, these findings have recently been challenged by a study suggesting that such toggling by climbing fiber inputs occurs predominantly in anaesthetized animals, and that Purkinje cells in awake behaving animals, in general, operate almost continuously in the upstate (Schonewille et al., 2006, Nature Neuroscience).
Findings have suggested that Purkinje cell dendrites release endocannabinoids that can transiently downregulate both excitatory and inhibitory synapses<ref> Kreitzer A & Regehr W, 2001. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WSS-4CC2XVR-15&_user=10&_coverDate=03%2F31%2F2001&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=17024408673ac673dfc51d3dd0b66c00 Retrograde Inhibition of Presynaptic Calcium Influx by Endogenous Cannabinoids at Excitatory Synapses onto Purkinje Cells]. Neuron Mar;29(3):717-27.</ref>
==Medical conditions related to Purkinje cells==
In humans, Purkinje cells are affected in a variety of diseases ranging from toxic exposure (alcohol, lithium), to autoimmune diseases and to genetic mutations (spinocerebellar ataxias, [[autism]]) and neurodegenerative diseases that are not thought to have a known genetic basis (cerebellar type of multiple system atrophy, sporadic ataxias).
In some domestic animals, a condition where the Purkinje cells begin to atrophy shortly after birth, called [[Cerebellar abiotrophy]], can lead to symptoms including [[ataxia]], intention tremors, hyperreactivity, lack of menace reflex, stiff or high-stepping gait, apparent lack of awareness of wherein the feet are (sometimes standing or walking with a foot knuckled over), and a general inability to determine space and distance.{{Fact|date=March 2007}} A similar condition known as [[cerebellar hypoplasia]] occurs when Purkinje cells either fail to develop in utero or die off in utero prior to birth. Ataxia-Telangiectasia is a genetic condition, in which Purkinje cells are progressively lost.
==Links==
*[http://www.antibodypatterns.com/ Cerebellar disoders]
*[http://www.ii.bham.ac.uk/clinicalimmunology/Neuroimmunology/ Disorders of cerebellum]
==References==
* Llinas R. and Hess, R. (1976) Proc. Natl. Acad. Science US 73: 2520-2523.
* Llinas R. and Sugimori M. (1980) J. Physiol. 305: 171-195
* Llinas R. Sugimori M. and Cherksey B. (1989) Annals of the New York Acad. Science 560:103-111
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{{Cerebellum}}
[[Category:Neurons]]
[[Category:Cerebellum]]
[[Category:CNS neurons]]
[[ca:Cèl·lula de Purkinje]]
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